DE19910886B4 - Method for producing a shallow trench isolation for electrically active components - Google Patents

Abstract

A method for making a shallow trench isolation for electrically active devices in crystalline silicon by dry etching, the shallow trench isolation having sloped sidewalls prepared by dry etching with a mask by using process gases with enhanced polymer formation to passivate the sidewalls of the trench, comprising the steps :
- Trenching by dry etching with a gas mixture of NF3, CHF3, N2 with a predominant proportion of CHF3 and low NF3; and below
- Rounding the corners at the transition from the bottom of the trench to the side walls by dry etching with a gas mixture of NF3, CHF3, N2 with a predominant proportion of NF3.

Description

The The invention relates to a method for producing a shallow trench isolation (Shallow trench isolation) for electrically active components in crystalline silicon.

at The production of semiconductor chips on wafers they are known to undergo a variety of process steps for structuring the semiconductor chips. One takes place one after the other Layer structure with subsequent structuring. For the layer structure For example, CVD process steps come and for structuring photolithographic process steps in conjunction with dry into consideration. During structuring, a photoresist is exposed and this in a subsequent etching process and at least under the photoresist layer is structured.

A Series of these process steps must be at very high process temperatures accomplished be in which the wafer a considerable heat stress, in particular during the Heating and cooling phases is suspended. This creates mechanical stresses in the wafer, which may cause errors in the crystal lattice structure. At Such places create stress concentration points, the trigger for the formation of displacements. Such dislocations can then to electrical defects, z. B. leakage currents lead. Cause these leakage currents a reduced charge retention time (retention time), so that the active Components (transistor, memory cell) are limited in their function.

In The modern CMOS technology is the isolation of the electrical active components with the help of shallow isolation trenches, ie a shallow trench isolation (STI). The production of this STI takes place by dry etching and subsequent replenishment with an oxide as insulator. Subsequently, the wafer by chemical planarized mechanical polishing (CMP), after which then the further structure structure can take place.

Shallow trench isolations are for example off US 5 807 789 A (Such Shallow Trench Isolations are also used for the lateral isolation of semiconductor memory cells with trench capacitors (see US 5,389,559 A . US 5,545,583 A . US 5,360,758 A . DE 197 03 611 A1 ), wherein the shallow trench isolations are at least partially produced in the silicon substrate. Etching methods for etching silicon are, for example, in US 5,770,484 A. . US 4 729 815 A . JP 05 259 269 A . EP 0 200 951 A2 . US 4,855,017 . JP 61 247 032 A and the article by M. Tsuchiaki et al., "Impact of Reactive Ion Etching Induced Carbon Contamination on Oxidation of Silicon", J. Electrochem. Soc., Vol. 143, no. 7, July 1996, pages 2378-2387, where from the cited references US 4 729 815 A and EP 0 200 951 A2 it is known to use CHF3, NF3 and N2.

The Dry etching over a Mask determines the shape, as well as width and depth of the STI, where the trench at least on the ground between floor and wall an angle of about 90 ° and so has sharp edges. These edges can be starting points for the described disorders be in the crystal lattice structure.

Of the The invention is therefore based on the object, an improved method to create a shallow trench isolation for memory cells, in the emergence of disorders is reliably prevented in the crystal lattice structure.

The The problem underlying the invention is achieved by a method according to claim 1 solved.

With Such a flat trench insulation produced in this way can arise of disorders be reliably prevented in the crystal lattice structure. The Realizing a continuous transition can be easy Means during the dry etching process the STI, the transition between the floor and the side walls is rounded off.

According to the invention points the ditch for the Shallow trench isolation taped, d. H. bevelled sidewalls on, so that the Angle between the floor and the side walls is 75 ° <a <90 °.

at such a trench isolation is the emergence of disturbances in the crystal lattice structure reliably prevented. Farther have taped sidewalls the particular advantage that the after dry etching necessary filling up of the STI is significantly improved with an oxide.

According to the invention is a combination of edge rounding in connection with manufacturing tapered sidewalls intended.

• – Herstellen des Trenches durch Trockenätzen mit einer Gasmischung aus NF3, CHF3, N2 mit einem überwiegenden Anteil von CHF3 und wenig NF3; und nachfolgend
• – Verrunden der Ecken am Übergang vom Boden des Trenches zu den Seitenwänden durch Trockenätzen mit einer Gasmischung aus NF3, CHF3, N2 mit einem überwiegenden Anteil von NF3.

Specifically, the object of the invention is achieved by a method for producing a shallow trench isolation for electrically active devices in crystalline silicon by dry etching, wherein the shallow trench isolation has beveled side walls, which are prepared by dry etching with a mask, by passivation of the side walls of the trench Process gases are used with increased polymer formation, comprising the steps:

• - Preparation of Trenches by dry etching with a gas mixture of NF3, CHF3, N2 with a predominant share of CHF3 and little NF3; and below
• - Rounding the corners at the transition from the bottom of the trench to the side walls by dry etching with a gas mixture of NF3, CHF3, N2 with a predominant proportion of NF3.

there be as process gases CHF3, NF3 and N2 are used, with additionally a dry etching by magnetic reinforced reactive ion etching with ICP (Inductive Coupled Plasma Source) or with ECR (Electrical Cyclotron Resonance) can be provided.

In a variant of the method according to the invention is used for dry etching used a taped mask.

According to the inventive method is after the preparation of the taped trench by dry etching a Rounding of the corners at the transition made from the bottom of the trench to the side walls.

The dry for rounding the corners is doing with a gas mixture of NF3, CHF3, N2 with a predominant Share of NF3 made.

At the inventive method the dry etching takes place with a gas mixture of NF3, CHF3, N2 with a predominant Share of CHF3 and little NF3.

The Invention will be explained in more detail below using an exemplary embodiment. In the associated Drawings show:

1 a shallow trench isolation according to a non-inventive example with rounded edges on the ground; and

2 a shallow trench isolation produced according to the invention with rounded edges on the bottom and additional beveled sidewalls.

As can be seen from the accompanying drawing figures, the bottom B of the shallow trench isolation trench STI is designed so that it continuously merges into the side walls SW. Preferably, the transition between the floor and the side walls is rounded ( 1 ). Although this already a substantial degradation of thermally induced stresses in the crystal lattice structure of the polycrystalline and crystalline silicon can be achieved, the invention provides for the trench for the shallow trench isolation additionally provided with tapered, ie bevelled side walls. The angle a between the bottom and the side walls SW should be between 75 ° <a <90 °. A particular advantage of taped sidewalls is also seen in the improved geometry for filling the trench with an oxide.

Both inventive measures can be used together.

The inventive production Trench isolation will be explained in more detail by an example. In this example, the trench isolation serves to isolate two adjacent trench capacitors etched into the Si substrate and formed a capacitor dielectric and a collar at the bottom or upper trench wall are filled with polysilicon. The trench isolation overlaps the trench capacitors partially, as shown in the figures.

To will be in this case first the pad nitride PN (Si3N4), possibly also other residues of a trench etching mask, and subsequently the polycrystalline and crystalline silicon with high selectivity to the resist mask etched. With the same etching rate must also the Collar C etched become. The production of the STI can be in a multi-level or also a one-step process. These are used for dry etching of tapped sidewalls of the STI as process gases CHF3, NF3 and N2 are used, with additionally a dry etching by magnetic reinforced reactive ion etching can be provided. additionally can dry-dry a taped mask can be used.

Afterwards will be a rounding of the corners at the transition from the bottom of the trench to the side walls performed. That for this intended dry etching is doing with a gas mixture of NF3, CHF3, N2 with a predominant Proportion of NF3 made so that an isotropic process control achieved becomes.

The dry with a process control with reinforced Passivation is using a gas mixture of NF3, CHF3, N2 with a predominant Share of CHF3 and little NF3 made.

following is the etched Digging with silica, for example with TEOS, filled. In many cases will prior to further structure building a planarization using CMP carried out, at the on the surface of the (mono) crystalline Si substrate yet located layers (here the whole surface applied TEOS and preferably also the pad-nitride layer) preferably completely be removed.

Claims (3)

Method for producing a shallow trench isolation for electric active components in crystalline silicon by dry etching, wherein the shallow trench isolation has beveled sidewalls which are dry etched with a mask are made by passivation of the side walls of the Trenches process gases with reinforced Polymer formation can be used, comprising the steps: - Produce Trenches by dry etching with a gas mixture of NF3, CHF3, N2 with a predominant Share of CHF3 and little NF3; and below - rounding the corners at the transition from the bottom of the trench to the side walls by dry etching with a gas mixture of NF3, CHF3, N2 with a predominant fraction of NF3. Method according to claim 1, characterized in that that this dry by magnetic field enhanced reactive ion etching with ICP or ECR. Method according to claim 1 or 2, characterized that to dry a taped mask is used.